basics_of_computer_aided_process_control.pptx

7/27/2019 Basics_of_computer_aided_process_control.pptx

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Basics of computer aided

process control


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Introduction

Figure: Computer in a Plant Control

In 1950, Brown & campbell proposed use of computer in processcontrol.In 1954, computer was used for real time in air borne application

Digitrac digital computer was used


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First Industrial computer control system called RW-300 (Ramo-Woolridge Company) was installed at Port Arthur refinery of TexacoCompany in Texas which achieved closed loop in march 1959.

The first direct digital control (DDC) computer system was FerrantiArgus 200 system installed in November 1962 at ICI ammonia sodaplant at Fleetwood, Lancashire.

1959 1962 : The early period1963 1974 : Centralized computer control ( Mainframe and mini

computer architecture)1975 onwards : Advent of the microprocessor and distributedcomputer control system.


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Role of Computer in Process Control

Two major applications Passive applications Acquiring Monitoring Alarming Data reduction systems

Active applications Above all and manipulation of process as well Optimization of process


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Figure : Digital dataacquisition


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Elements of computer aided processcontrol

Basics functions of computer aided process control1. Measurements and data acquisition

2. Data conversion with scaling and checking

3. Data accumulation and formatting

4. Visual display

5. Comparing with limits and alarm rising

6. Recording and monitoring of events, sequences and trends

7. Data logging and computation8. Control actions


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Computer Aided Process Control

Figure: Typical computer aided process control system


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Computer Aided control of hot airblower


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Classification of computer aidedprocess control

1. Batch or Sequential Process

2. Continuous control

3. Supervisory control4. Direct Digital control .


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Batch process

Figure : Chemical reactor ( batch reactor)


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Classification of batch process

Based on the number of products1. Single product batch process

2. Multi grade batch process

3. Multi product batch process Based on the structure of the process facility

1. Serial (Single Stream) Structure batch process

2. Parallel (Multi stream) Structure batch process

3. Serial/parallel structure batch process


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Structure based batch process


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Complexity of batch processes


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Differences between batch and continuousprocess

Discrete loads are fed in batch process whereas continuous loads in continuous process Each batch of material being processed can be identified easily in batch process where as it

is difficult in case of continuous processes. Each batch of raw material can be processed differently in various parts of the process.

Same equipment can be used for different products or different grade of products. Movement of batch from one equipment to another can occur only when the operation in

that equipment is complete and the next equipment is ready to receive the material.Whereas continuous process materials flow is steadily from one equipment to the next.


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Supervisory Computer controlprocess

Three general types of optimization problems areencountered in industrial process operations1. Operating conditions ( such as reactor temperature,

reflux ratio, etc., in refinery operations)

2. Allocation, i.e., optimal distribution of a limitedresource among several parallel (alternative) processunits ( such as fuel use, feedstock selection, etc.)

3. Scheduling i.e., batch processing , cleaning,maintenance , relining.


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Supervisory Computer controlsystem


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Direct digital control(DDC)processes

In 1962 Imperial Chemical Industries (ICI) inEngland replaced complete analoginstrumentation for process control by

Ferranti Argus computer. The computer considered 224 variables and

controlled 129 valves directly. DDC is also called loop control, the functions

of comparator , controller , limiting and othersafe guarding operations are provided by thedigital computer itself.


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DDC for chemical reactor system


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DDC software


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DDC drawbacks If only one processor was used , a

single failure could affect a largenumber of controlled variables andpossibly disable an entire process.


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Computer aided process controlarchitecture

Centralized computer control Distributed computer control Hierarchical computer control


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Centralized computer controlsystems

Early computer control had many limitationssuch as

slow magnetic drum memory,

very small memory size,programming to be done in machine language whichwas very difficult to program,

Little or no experience of the supplier and the use in

computer applicationsUnreliable computer hardware and software, etc.


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Centralized computer controlsystems

Use of centralized computer also suffered from problemssuch as

Expensive requirement of large communication systems tobring the plant (field) signals to the centralized computer

location and output control signals to the field devices, electrical noise problems for large distance communication

of signals, Complete stoppage of plant/process in case of failure of the

centralized computer system, communication system, etc,.


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Distributed computer controlsystems

DCCS became popular as opposed to acentralized computer control system and thelimitations of centralized computer controlsystem were removed.

In 1969, Honeywell company, USA, designed TDC 2000 system, a distributed computercontrol system as an alternative to the

unwieldy and unreliable centralized computercontrol system.


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Distributed digital controlarchitecture


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Features of Distributed computercontrol systems


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Hierarchical computer controlsystems


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Hierarchical computer controlarchitecture


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Tasks of computer control systems


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Tasks of computer control systems


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Man Machine Interface


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Benefits of using computer inprocess control

basics_of_computer_aided_process_control.pptx

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